Heavy data consumption

I have bought the new iPhone 6s at the Apple Store in Paris Louvres on October 2, then updated it to the new latest version of IOS9.0.2.

This last weekend, I suddenly started observing a abnormally heavy consumption of data (about 13GB in a couple of days, while my usual consumption is 3GB a month.

First I was told that I needed to turn off the "wifi Assist" button to avoid unnecessary consumption, which I did. Then I was told to close down application and I closed most, yet it not help.

I checked under 'Settings', then 'Cellular" then 'System Services' and saw that under 'general' I had consumed 13.1 Gb in a couple of days. I checked further and saw that the "Hey Siri" was on, I turned it off just now.

I took the telephone to the technical department of the local operator (TOUCH in Lebanon) and they say that these things can happen and that the solution is in installing and then re-installing the IOS 9.0.2 .

I find this strange, I am on my 5th Iphone so far and never heard of such a problem which has cost me so far close to 200$ in over consumption without my knowledge.

Kindly assess the problem and revert to me with a solution.

Thank you

Ralph Eid